JPH06295425A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a tape excellent in electromagnetic transducing characteristics and having satisfactory running property especially as a digital audio tape when a coating type magnetic recording medium is formed by coating a base film with a magnetic coating material. CONSTITUTION:A magnetic coating material is prepd. using magnetic powder free from pores and having 30-40m<2>/g BET specific surface area. A base film is coated with the coating material to form a magnetic layer having >=55,000A/m coercive force Hc and <=20nm surface roughness and a digital audio tape excellent in electromagnetic transducing characteristics and running property is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating on a non-magnetic support, and more particularly to a digital audio tape.

[0002]

2. Description of the Related Art With the development of equipment, magnetic recording media tend to have higher recording densities, and are changing from conventional analog recording to digital recording. The wave of digitization is not only for business use but also for consumer use. Is definitely spreading. In the audio field, analog cassette compact cassettes (hereinafter abbreviated as CC) have been at the top of the list for many years, but digital audio tape recorders (hereinafter D
(Abbreviated as AT) was developed, and the digitization became reliable. However, the DAT has a structure similar to that of a VTR in which the head is installed on a rotating cylinder similar to a conventional video tape recorder (hereinafter abbreviated as VTR), and the tape running mechanism winds a tape around the cylinder to record and reproduce. Therefore, it is supposed that only DAT dedicated tape can be used. Further, due to the copyright problem caused by digital recording, it has not been widely used yet. Therefore, there has been a demand for the development of a compatible system capable of digital recording while making use of the vast amount of conventional CC. As a result, the development of fixed type multi-channel heads has progressed by applying the semiconductor thin film forming technology, and further, the digital compact cassette system has been proposed due to the development of the signal compression technology, and a new high-performance digital compact cassette corresponding to the system is proposed. Deck (hereinafter D
(Abbreviated as CC) was developed and commercialized.

Considering a system capable of digital recording while maintaining compatibility with the conventional CC, the head remains fixed, the tape width is 3.78 mm, and the relative speed between the head and the tape is 4.76 cm / sec. High density recording must be achieved under the condition. For that purpose, it is expected that short wavelength recording with the shortest recording wavelength of 1 μm or less and narrowing of track by multi-channeling of the head.
In such a system, the tape is also required to have magnetic energy capable of high recording density and have a smooth magnetic layer surface.

[0004]

Metal magnetic powder has been conventionally used for designing a tape having a high recording density.
DAT tapes and CC metal tapes have been commercialized. In the case of a DAT laminated amorphous head or a CC permalloy bulkhead, if a recording current is improved and set to an appropriate value, recording can be sufficiently performed even on a tape having a high coercive force Hc such as a metal tape. In, the characteristics equivalent to those of the CD (compact disk) are obtained, and in CC, the output improvement in the high frequency band (12 kHz) is achieved. However, in the case of DCC, since a thin film multi-channel head is used, if the coercive force of the medium is set too high, the head will be magnetized and saturated, and sufficient recording will not be possible and the required electromagnetic conversion characteristics will not be obtained. . Further, the overwrite characteristic is also deteriorated, and in a severe case, the error rate is deteriorated.

In order to form a smooth surface magnetic layer, magnetic powder must be made into fine particles and highly dispersed, and a smooth base film must be adopted. In DAT, fine metal powder and smooth base film have already been adopted. A magnetic layer having a smooth surface is formed. However, in the DCC for the purpose of upward compatibility with CC, it is difficult to use the metal magnetic powder because of the reasons described above, and the traveling system is D
Since it is completely different from the case of AT, using a too smooth base film causes a problem in running property. For this reason, conventionally, no media using fine particle magnetic powder or a smooth base film has been developed in CC, and magnetic powder in consideration of these factors has been required in DCC.

The magnetic powder produced by the conventional manufacturing method cannot avoid the generation of voids, and the porous magnetic powder not only adversely affects the magnetic properties but also does not increase the particle density, resulting in agglomeration of particles when used as a paint. However, the dispersibility decreases, the orientation deteriorates, and the magnetic characteristics of the medium deteriorate. In addition, since the BET value becomes large due to the large pores, a large amount of resin is required to disperse the particles, and the amount of lubricant adsorbed also increases.

In view of the above problems, the present invention has good dispersibility, can be highly filled in a magnetic paint, and can be used in a thin film head capable of digital recording, and can obtain good electromagnetic conversion characteristics and can be run. It is intended to provide a digital audio tape having excellent durability.

[0008]

In order to solve the above problems, the present invention provides a magnetic recording medium comprising a magnetic layer containing magnetic powder, a binder and the like formed on a specific magnetic support. The magnetic powder of the recording medium is a non-pore type magnetic powder with no pores on the surface and has a specific surface area of 3 by the BET method.
0 to 40 m ² / g of Co-γ-Fe ₂ O ₃ magnetic powder is used,
The coercive force Hc of the magnetic layer is 55000 A / m or more, and the surface roughness of the magnetic layer is 20 nm (RMS) or less, which is an essential condition.

[0009]

According to the structure of the present invention, it is possible to obtain a DCC tape which is compatible with CC and is compatible with a digitally recordable DCC system. By controlling the surface state of the magnetic powder, even a thin-film multi-channel head can sufficiently record without magnetization saturation. Further, by setting the specific surface area to an appropriate size and setting the surface property of the magnetic layer, sufficient output can be secured even in the short wavelength region where the recording wavelength is 1 μm or less, and good runnability can be obtained.

According to the study of the present inventors, the magnetic powder used
It is desirable that the surface state of is non-pore. Pore
Optimum magnetic properties due to low particle density when using magnetic powder
Is not obtained, fusion between particles occurs and dispersion is poor.
Therefore, the orientation is not sufficient. Non-pore Co-γ-F
e₂O₃The magnetic powder has a low oil absorption, and the particles are not filled in the tape coating film.
Tape with high filling amount and high maximum magnetic flux density (Bm)
can get. Moreover, the orientation ratio (0.R.) is high and the squareness ratio (S.
R.) becomes higher. In addition, because it is a non-pore,
At this time, particles are less likely to be broken or damaged, and the original high retention of particles is maintained.
Sufficient paint dispersion can be achieved without impairing the magnetic force. Therefore resin
It is also possible to reduce the amount and disperse over a high share.
It becomes Noh. The specific surface area of the magnetic powder used is the BET method.
At 30-40m ²/ G, the surface roughness of the created tape is 2
It is preferably 0 nm or less. The specific surface area of the magnetic powder
If the output is not suitable or the surface of the tape is rough, the output
Not only that, but also the runnability deteriorates, powder falls, etc.
Causes the problem.

[0011]

EXAMPLES Examples of the present invention will be described below.

The ferromagnetic powder used in the present invention is a needle-shaped fine powder of metal oxide such as γ-Fe ₂ O ₃ , CrO ₂ and Co-deposited γ-Fe ₂ O _3. ,
Alternatively, ferromagnetic metal powders such as Fe, Fe-Co, and Fe-Co-Ni can be used. In particular, with regard to these ferromagnetic metal powders, those containing a trace amount of additional elements such as Al, Cr and Si can also be used in consideration of weather resistance or prevention of sintering during manufacturing.

The binder resin used in the present invention includes vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, polyurethane resin, polyester resin. Acrylonitrile-butadiene copolymer, cellulose-acetate-butyrate, epoxy resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin and the like are preferably used.

Aluminum oxide, chromium oxide, iron oxide, and silicon oxide are added to the magnetic layer as a reinforcing agent and an abrasive, higher fatty acids and fatty acid esters are used as lubricants, and carbon black is used as an antistatic agent. It is also possible to add.

Further, a magnetic coating material is prepared by dispersing the constituent materials of the magnetic layer in an organic solvent, and this is coated on a non-magnetic base film. In this case, the solvent of the magnetic coating material is a ketone (eg acetone, Methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), alcohols (eg methanol, ethanol,
Propanol, butanol, etc.), esters (eg methyl acetate, ethyl acetate, ethyl lactate, glycol acetate, monoethyl ether etc.), glycol ethers (eg ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane etc.), aromatic carbonization Examples thereof include hydrogen (eg, benzene, toluene, xylene, etc.), aliphatic hydrocarbons (eg, hexane, heptane, etc.), nitropropane and the like.

The base film to which the magnetic paint is applied is non-magnetic and includes polyester (eg polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene naphthalate etc.), polyolefin (eg polypropylene, polyethylene etc.), cellulose derivative (eg cellulose). Suitable examples include triacetate, cellulose diacetate, etc.), polyvinyl chloride, polyimide, polyamide and the like. Examples will be described in detail below.

Example 1 As a magnetic powder, a ferromagnetic metal powder having a BET specific surface area value of 34 m ² / g was used, and as a binder resin, a polyurethane resin and a polyvinyl chloride copolymer resin were mixed. I used one. Fatty acids and fatty acid esters are used as the lubricant, alumina is used as the abrasive, and methyl ethyl ketone is used as the organic solvent used for the coating solvent.
Aromatic hydrocarbons such as toluene and cyclohexanone were used.

[0018]

[Table 1]

First, the magnetic powder, the antiwear agent and the initially added solvent are mixed by stirring for 1 hour in a planetary mixer. The binder resin is slowly added over 2 hours, and after the addition, the mixture is stirred and mixed for 1 hour. Further, the solvent was added over 2 hours to make the kneaded material into a large lump, and after confirming that the power consumption of the kneader was maximized, the kneading was continued for 8 hours. The remaining solvent is added dropwise over 3 hours to dilute and reduce the solid content concentration. An abrasive was added to this and further dispersed using a sand grinder to obtain a magnetic paint. Lubricants and hardening agents were added to this, and it was passed through a 0.4 μm filter (HT-40 manufactured by Nippon Roki Co., Ltd.) to obtain 10 μm.
m-thick PET (surface roughness = 15 nm), coated with magnetic field, dried, and then super calender (surface treatment machine)
After the surface treatment of the magnetic layer, a curing treatment is performed at 60 ° C. for 24 hours. Further, a back coat layer containing carbon black as a main component was coated on PET on the side opposite to the magnetic layer, and 3.8 was applied.
An audio tape was produced by cutting it to a width of mm.

(Example 2) In (Table 1) of Example 1, the magnetic powder was replaced with Co-γ- with a BET specific surface area of 30 m ² / g.
An audio tape was produced in the same manner as in Example 1 except that Fe ₂ O ₃ was used.

(Example 3) In Table 1 of Example 1, the magnetic powder was Co-γ- with a BET specific surface area of 39 m ² / g.
An audio tape was produced in the same manner as in Example 1 except that Fe ₂ O ₃ was used.

(Comparative Example 1) In (Table 1) of Example 1, the magnetic powder was changed to Co-γ-Fe ₂ O ₃ having a BET specific surface area of 40 m ² / g and pores. Then, an audio tape was produced.

(Comparative Example 2) In (Table 1) of Example 1, the magnetic powder was changed to Co-γ-Fe ₂ O ₃ having a BET specific surface area of 33 m ² / g and pores. Then, an audio tape was produced.

Comparative Example 3 With the same composition as in Example 1, a base film made of PET having a surface roughness of 20 nm was used.
An audio tape was produced in the same manner as in Example 1.

(Comparative Example 4) In Example 1 (Table 1), the magnetic powder was prepared as in Example 1 using Co-γ-Fe ₂ O ₃ having a BET specific surface area of 45 m ² / g and pores. An audio tape was produced in the same manner. However, the total dispersion time was about 2/3 of that in Example 1.

Comparative Example 5 Using the magnetic powder of Comparative Example 2,
A magnetic coating material was prepared in the same manner as in Comparative Example 4, coated on the same PET as in Comparative Example 3, and thereafter an audio tape was prepared in the same manner as in Example 1.

The measurement results of various characteristics of the audio tapes obtained in each of the above Examples and Comparative Examples are summarized in (Table 2).

[0028]

[Table 2]

The evaluation method is shown below. (1) Magnetic Properties (Hc) Using a vibrating sample magnetometer manufactured by Toei Industry Co., Ltd., measurement was performed at a maximum magnetic field of 398100 A / m and a sweep speed of 1 min. (2) Surface Roughness Using a non-contact three-dimensional surface roughness measuring machine of WYKO, 50
The surface shape was measured in a μm × 50 μm region, and the result was expressed as root mean square surface roughness (rms). (3) Electromagnetic conversion characteristics Using a commercially available audio deck (M95 manufactured by Matsushita Electric Industrial Co., Ltd.), the head is changed from the existing permalloy bulkhead to a thin film multi-channel head, and the circuit is modified for DCC, with the running system as it is. , The output level at 48 kHz, and the noise level and C at 30 kHz
/ N (48 kHz / 30 kHz) was measured. All measured values are shown as 0 dB in Example 1. (4) Overwrite characteristics A commercially available audio deck (M95 manufactured by Matsushita Electric Co., Ltd.) is used (the head and circuit are modified in the same manner as above), 9.6k
A signal level of 9.6 kHz is shown when a Hz signal is input and 48 kHz is input thereon. All measured values are shown as 0 dB in Example 1. (5) Powder removal A commercially available audio deck (M95 manufactured by Matsushita Electric Co., Ltd.) was used to determine the powder removal state when the tape was run for 100 passes, at the following levels. The case where no powder was completely dropped in the running system or the head area was set to 5, and the case where a large amount of powder was dropped was set to 1.

As is clear from (Table 2), according to the constitution of the present invention, as shown in the examples, non-porous Co-γ-Fe ₂
If O ₃ is used and the surface roughness is 20 nm or less, an electromagnetic tape having excellent electromagnetic conversion characteristics, good tape wear, and good running property can be obtained.

On the other hand, when the specific surface area of the magnetic powder is large as in the comparative example, the surface roughness of the magnetic layer is large and the electromagnetic conversion characteristics, particularly the output in the high range, is lowered and the C / N is deteriorated.
Even if non-pore or magnetic powder having pores is used, if the surface roughness of the base film is rough, the surface roughness of the finished tape will be poor and the output will be low in the high range. If the dispersion is not performed sufficiently, the tape will have low magnetic characteristics, and the electromagnetic conversion characteristics will not be sufficient, and the tape will have poor surface properties, resulting in poor runnability.

[0032]

From the results of the above table, a magnetic coating material was prepared using non-pore type Co-γ-Fe ₂ O ₃ having a BET value of 30-40 m ² / g as the magnetic powder,
For a medium having a magnetic layer Hc of 55000 A / m or more and a surface roughness of 20 nm or less, it is possible to supply an audio tape having excellent overwrite characteristics and excellent running performance, and the effect is very large. There is something.

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Claims (3)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a ferromagnetic powder, a binder and the like formed on a non-magnetic support, wherein the magnetic powder is a non-pore type Co-γ-Fe.
A magnetic recording medium characterized by using ₂ O ₃ . 2. The specific surface area of the magnetic powder is 30-4 by the BET method.
The magnetic recording medium according to claim 1, wherein the magnetic layer has a coercive force of 55000 A / m or more at 0 m ² / g. 3. The magnetic recording medium according to claim 1, wherein the surface roughness (rms) of the magnetic layer is 20 nm or less.